This invention relates to vacuum cleaners which have a cyclonic separation apparatus. In another aspect, the invention relates to an electrostatic precipitator.
Cyclone separators, which are sometimes referred to merely as cyclones, are devices that utilize centrifugal forces and low pressure caused by spinning motion to separate materials of differing density, size and shape. FIG. 1 illustrates the operating principles in a typical cyclone separator (designated by reference numeral 10 in FIG. 1). The following is a description of the operating principles of cyclone separator 10 in terms of its application to removing entrained particles from an air stream in a vacuum cleaner.
Cyclone separator 10 has an inlet pipe 12 and a main body comprising upper cylindrical portion 14 and lower frusto-conical portion 16. The particle laden air stream is injected through inlet pipe 12 which is positioned tangentially to upper cylindrical portion 14. The shape of upper cylindrical portion 14 and frusto-conical portion 16 induces the air stream to spin creating a vortex. Larger or more dense particles are forced outwards to the walls of cyclone separator 10 where the drag of the spinning air as well as the force of gravity causes them to fall down the walls into an outlet or collector 18. The lighter or less dense particles, as well as the air medium itself, reverses course at approximately collector G and pass outwardly through the low pressure centre of separator 10 and exit separator 10 via air outlet 20 which is positioned in the upper portion of upper cylindrical portion 14.
The separation process in cyclones generally requires a steady flow free of fluctuations or short term variations in the flow rate. The inlet and outlets of cyclone separators are typically operated open to the atmosphere so that there is no pressure difference between the two. If one of the outlets must be operated at a back pressure, both outlets would typically be kept at the same pressure.
When a cyclone separator is designed, the principal factors which are typically considered are the efficiency of the cyclone separator in removing particles of different diameters and the pressure drop associated with the cyclone operation. The principle geometric factors which are used in designing a cyclone separator are the inlet height (A); the inlet width (B); the air outlet diameter (C); the outlet duct length (D); the cone height (Lc); the dirt outlet diameter (G);and, the cylinder height (L)
The value d50 represents the smallest diameter particle of which 50 percent is removed by the cyclone. Current cyclones have a limitation that the geometry controls the particle removal efficiency for a given particle diameter. The dimensions which may be varied to alter the d50 value are features (A)-(D), (G), (L) and (Lc) which are listed above.
Typically, there are four ways to increase the small particle removal efficiency of a cyclone. These are (1) reducing the cyclone diameter; (2) reducing the outlet diameter; (3) reducing the cone angle; and (4) increasing the body length. If it is acceptable to increase the pressure drop, then an increase in the pressure drop will (1) increase the particle capture efficiency; (2) increase the capacity and (3) decrease the underflow to throughput ratio.
In terms of importance, it appears that the most important parameter is the cyclone diameter. A smaller cyclone diameter implies a smaller d50 value by virtue of the higher cyclone speeds and the higher centrifugal forces which may be achieved. For two cyclones of the same diameter, the next most important design parameter appears to be L/d, namely the length of the cylindrical section 14 divided by the diameter of the cyclone and Lc/d, the length of the conical section 16 divided by the width of the cone. Varying L/d and Lc/d will affect the d50 performance of the separation process in the cyclone.
Due to its intended use, a vacuum cleaners is designed to filter particles of varying sizes from an air stream. With most vacuum cleaners on the market, a filter material such as a paper bag is used to filter the air. The bag will remove from the air stream any particle larger than the size of the pore in the bag. Thus only a single stage of filtration may be employed. However, if a cyclone is used in a vacuum cleaner, then multiple filtration stages may be employed. This is due to the fact that particle sizes which are generally to be filtered by a vacuum cleaner take on a spectrum of values that necessitates that a plurality of cyclonic separators be used in a series. For example, the first cyclonic separator in a series may have a large d50 specification followed by one with a smaller d50 specification.
For example, in U.S. Pat. No. 3,425,192, a vacuum cleaning assembly was disclosed which used a first frusto-conical cyclone and six secondary cyclones.
More recently, cyclonic technology has been improved and introduced commercially into canister and upright vacuum cleaners. See for example U.S. Pat. No. 4,593,429. This patent discloses a vacuum cleaner design in which sequential cyclones are utilized as the filtration medium for a vacuum cleaner. Pursuant to the teaching of this patent, the first sequential cyclone is designed to be of a lower efficiency to remove only the larger particles which are entrained in an air stream. The smaller particles remain entrained in the air stream and are transported to the second sequential cyclone which is frusto-conical in shape. The second sequential cyclone is designed to remove the smaller particles which are entrained in the air stream. If larger particles are carried over into the second cyclone separator, then they will typically not be removed by the cyclone separator but exit the frusto-conical cyclone with the air stream.
One disadvantage of cyclonic vacuum cleaners is the amount of power which is required to create an air flow sufficient to convey the dirty air through the cyclones at sufficient speeds to maintain the air flowing cyclonically through the cyclones.
In order to achieve high levels of particle removal, cyclonic vacuum cleaners which are currently on the market incorporate a HEPA(trademark) filter. Such filters are effective in removing small particulate matter from the air stream so that the air which exits the vacuum cleaner is essentially for refiltered. One disadvantage of such HEPA(trademark) filters is that they provide substantial resistance to the flow of air there through. By removing the HEPA(trademark) filter, the pressure drop which occurs during the passage of the air through the filter assembly of a vacuum cleaner may be reduced by, eg., up to 20%. Accordingly, by removing the HEPA(trademark) filter, the flow rate through the vacuum cleaner may be substantially increased and/or the size of the motor may be reduced by eg., up to 20%. However, the amount of particulate matter which will be contained in the dirty air stream will be increased.
The instant invention provides an alternate approach to the use of such HEPA(trademark) filters. Electrostatic filters generally provide minimal resistance to the flow of air and accordingly do not generally provide much of the pressure drop as an air stream passes there through. The electrostatic filter may be designed to remove the same size particles as are removed by the HEPA(trademark) filter which is currently in use. Alternately, the electrostatic filter may be designed to remove even larger particles. Accordingly, by using an electrostatic filter, the pressure drops for a vacuum cleaner may be substantially reduced (compared to a vacuum cleaner using a HEPA(trademark) filter). Further, the electrostatic filter may provide enhanced particle remover compared to even a HEPA(trademark) filter and accordingly the clean air outlet from the vacuum cleaner may produce air which is even cleaner than that which is achieved from commercially available cyclonic vacuum cleaners which even incorporate at HEPA(trademark) filter.
In accordance with the instant invention, there is also provided a vacuum cleaner comprising:
(a) a dirty air inlet for receiving air containing dirt;
(b) a clean air outlet spaced for the dirty air inlet;
(c) an air flow path extending downstream from the dirty air inlet to the clean air outlet; and,
(d) a filtration assembly positioned in the air flow path, the filtration assembly comprising:
(i) at least one cyclonic cleaning stage in flow communication with the dirty air inlet and having a partially cleaned air outlet; and,
(ii) at least one electrostatic precipitator positioned in the air flow path downstream from the at least one cyclonic cleaning stage and upstream of the clean air outlet; and,
(f) an on board power source comprising at least one battery for operating the vacuum cleaner.
In one embodiment, the at least one cyclonic cleaning stage comprises at least a first cyclonic cleaning stage and a second cyclonic cleaning stage downstream from the first cyclonic cleaning stage.
In another embodiment, the at least one electrostatic precipitator is positioned in the air flow path downstream from the first cyclonic cleaning stage and upstream of the second cyclonic cleaning stage.
In another embodiment, the at least one electrostatic precipitator is positioned in the air flow path downstream from the second cyclonic cleaning stage and upstream of the clean air outlet.
In another embodiment, the first cyclonic cleaning stage comprises one cyclone and the second cyclonic cleaning stage consists of from two to five second cyclones.
In another embodiment, the second cyclonic cleaning stage removes particulate material larger than that which is removed by the at least one electrostatic precipitator.
In another embodiment, the at least one cyclonic cleaning stage comprises a cyclone chamber removably mounted in a housing and the at least one electrostatic precipitator comprises an electrostatic precipitator removably mounted in the cyclone chamber.
In another embodiment, the cyclone chamber has an air outlet and the electrostatic precipitator is positioned in the air outlet of the cyclone chamber.
In another embodiment, the cyclone chamber has an air outlet and the electrostatic precipitator is removably mounted in the air outlet of the cyclone chamber.
In accordance with the instant invention, there is provided a vacuum cleaner for receiving and cleaning a dirty air stream to obtain clean air comprising:
(a) first means for cyclonically treating the dirty air stream to obtain a partially cleaned air stream;
(b) electrostatic precipitation means positioned downstream from the first means for cyclonically treating a dirty air stream; and,
(c) an on board power supply means comprising battery means for operating the vacuum cleaner.
In one embodiment, the vacuum cleaner further comprises second means for further cyclonically treating the dirty air stream positioned downstream from the first means for cyclonically treating a dirty air stream.
In another embodiment, the electrostatic precipitation means is positioned in the air flow path downstream from the first means for cyclonically treating the dirty air stream and upstream of the second means for further cyclonically treating the dirty air stream.
In another embodiment, the electrostatic precipitation means is positioned in the air flow path downstream from the second means for further cyclonically treating the dirty air stream and upstream of the clean air outlet.
In another embodiment, the second means for further cyclonically treating the dirty air stream removes particulate material larger than that which is removed by the electrostatic precipitation means.
In another embodiment, the first means for cyclonically treating the dirty air stream is removably mounted in a housing and the electrostatic precipitation means is removably mounted with the first means for cyclonically treating the dirty air stream.
In another embodiment, the first means is removably mounted in n the vacuum cleaner.
In accordance with the instant invention, there is also provided an electrostatic precipitator for separating chargeable particulate matter from a fluid stream comprising:
(a) a housing having at least one fluid inlet and at least one fluid outlet;
(b) at least one member movably positioned in the housing for generating a high voltage potential in response to the movement of the at least one member in the housing; and,
(c) a conductive member for transmitting the high voltage potential to particulate matter entrained in the fluid whereby particulate matter is oppositely charged to the at least one member prior to encountering the at least one member and is attracted to the at least one member during passage of the charged particulate matter through the housing.
In one embodiment, the electrostatic precipitator further comprises a directing member to cause the fluid to rotate the at least one member.
In another embodiment, the at least one member and at least a portion of the housing is constructed from a material that will produce a potential difference between the at least one member and the portion of the housing due to frictional contact of the at least one member with the housing as the at least one member moves in the housing due to the flow of fluid through the housing.
In accordance with the instant invention, there is also provided an electrostatic precipitator for separating chargeable particulate matter from a fluid stream comprising:
(a) housing means having fluid inlet means and fluid outlet means;
(b) individual chargeable means movably positioned in the housing means for generating a high voltage potential in response to the movement of the individual chargeable means in the housing means; and,
(c) conductive means for transmitting the high voltage potential to particulate matter entrained in the fluid whereby particulate matter is oppositely charged to the individual chargeable means prior to encountering the individual chargeable means and is attracted to the individual chargeable means during passage of the charged particulate matter through the housing means.
In another embodiment, the electrostatic precipitator further comprises a directing means to cause the fluid to rotate the individual chargeable means.
In another embodiment, the individual chargeable means and at least a portion of the housing means is constructed from a material that will produce a potential difference between the individual chargeable means and the portion of the housing means due to frictional contact of the individual chargeable means with the housing means as the individual chargeable means moves in the housing means due to the flow of fluid through the housing means.
As will be appreciated, the electrostatic filter may comprise the portion of the filter assembly of the vacuum cleaner to remove the smaller particles from the dirty air stream. For example, in a vacuum cleaner having first and second cyclonic separation stages, the first cyclonic separation stage is preferably configured to remove the coarsest particles from the air stream and the second cyclonic separation stage is preferably configured to remove the smallest particles from the air stream while the electrostatic filter is designed to remove particles having an intermediate size. Thus, if the second cyclonic separation stage is positioned after the electrostatic filter, then the second cyclonic separation stage may be configured to remove the particles which are not filtered by either the first cyclonic separation stage or the electrostatic filter. As the second cyclonic separation stage need not be designed to remove the finest particulate matter, it may be of a lower efficiency then would otherwise by useable and accordingly may have a larger diameter. By increasing the diameter of second stage cyclones, the pressure drop across each second stage cyclone will be reduced thereby producing a further reduction in the pressure drop which occurs by the passage of air through the filter assembly of the vacuum cleaner and further reducing the power (size of motor) which is required.
If the electrostatic filter is positioned between the first and second cyclonic separation stages, the finest particulate matter is removed prior to the second cyclonic separation stage treatment of the air. The removal of the fine particulate matter prior to this stage prevents this particulate matter from entering the second stage cyclones and contaminating the interior surface of the second stage cyclones.
In a further alternate embodiment, the first and second cyclonic separation stages may be positioned prior to the electrostatic filter.
In a further preferred embodiment, the electrostatic filter is removable so that it may be cleaned, such as by rinsing with water to remove the particulate matter which is collected thereon.